Week 2: Embryology Flashcards
Mammalian brains are all quite ____.
similar
Provide some examples of mammals.
rats, mice, cats, primates
Most experimental studies of the brain are done on which type of mammals?
rodents (rats/ mice)
What are some key differences between the rat and human brain?
- convolutions (rat brain very small)
- size of cerebral hemispheres
For the mostpart, the CNS of humans has ________ symmetry, meaning what?
bilateral symmetry.
This means the left and right hand sides are mirror images of each other; which is true for both the brain and spinal chord (for the most part, variation exists to small degree)
Explain what is meant by the following general terms:
ipsilateral
structures which are on same side
ie. left eye is ipsilateral with left ear
Explain what is meant by the following general terms:
contralateral
structures are on opposite sides
ie. left eye and right eye
The whole of the CNS is derived from the walls of a ____ filled ____.
fluid filled tube
The neural tube starts forming from what day post conception?
17/18
What are the 3 primary germ layers?
endoderm
ectoderm
mesoderm
What does the ectoderm form?
- epidermis
- hair
- nails
- nervous system
What does the endoderm form?
-lining viscera (digestive, respiratory)
-
What does the mesoderm form?
- CT (bones)
- muscle
What are the alternative name(s) for the primitive nervous system? Why?
neuroectoderm
OR
neural plate.
The NS develops from the ectoderm, thus the NS primal form may be referred to as the neuroectoderm.
This primal form is essentially just a band of ectodermal tissue that gives rise to the NS. Thus it may also be referred to as a neural ‘plate’.
Explain what is meant by the following general term(s):
neural plate
- flat sheet of cells
- forms by day 18 of embryo development
- initiated by notochord
- forms all neurophil
Explain what is meant by the following general term(s):
neurophil
- neurons
- astrocytes
- oligodendrocyte
- ependymal cells
The neural plate develops a neural groove, in a process known as _______.
neurulation
Neurulation occurs by what day?
day 20
Where does the neural groove exist?
Within the midline of neural plate, on the posterior surface.
- (germ layer)
Endoderm
- (germ layer)
Mesoderm
- (germ layer)
Ectoderm
1
Future Neural Crest
2
Neural plate and groove
3
Ectoderm
4
Mesoderm
5
Notochordal plate
6
Endoderm
At what day of embrological development would you expect this to be? why?
Day 18. Because the neural groove has not formed yet, the germ layers are still “flat” rather than forming the proper tube structure that will occur in the following days.
At what day of embryological development would you expect this to be? why?
Day 20. Because neuralation has occured; you can clearly distinguish the neural groove but no somites are present yet.
At what day of embryological development would you expect this to be? why?
day 21. Neurelation has occured AND development of somites has begun.
2
Neural groove
4
Mesoderm
5
Notochord
6
Endoderm
2
Neural tube
3
Neural Crest
1
Ectoderm
2
Neural Fold
3
Mesoderm
5
Endoderm
A
Rostral
B
Caudal
1
Prosencephalon
2
Mesencephalon
3
Rhombencephalon
4
Spinal Cord
Explain what is going on in this image
Neural Crest cells are migrating from a rostral to caudal/lateral direction to eventually form the cell types for the:
- Sensory neurons in spinal & some cranial nerve ganglia (CN V, VII, VIII, IX, X)
- Postganglionic neurons of ANS
- Schwann cells of PNS
- Adrenal medulla
- Some cartilage, bone and connective tissue
- pigment cells
1
Spinal Cord
2
Myencephalon
3
Metencephalon
4
Mesencephalon
5
Diencephalon
6
Telencephalon
7
Cervicle flexure
8
Cephalic flexure
9
pontine flexure
1
Forebrain
2
Telencephalic vesicles
3
Diencephalon
4
Optic vessicles
5
Midbrain
6
Hindbrain
Explain what is happening in this image.
The disproportionate growth of cortex is creating a c-shape
4
Cerebellum
5
Fourth ventricle
6
Pons
4
Tectum
5
Cerebral Aquaduct
6
Tegmentum
4
Fourth ventricle
5
Medulla
6
Medullary pyramids
1
Epyndyma
2 (what is it and what will it become)
Alar plate: will become dorsal horn
3
Sulcus Limitans
4 (what is it and what will it become)
Basal Plate: Will become ventral horn
How does the neural groove deepen?
as the neural plate folds inwards
After the neural fold deepens, the walls of the neural groove begin to form whats known as _____ _____.
neural folds.
Briefly explain how & when the neural tube develops?
By day 22, the neural folds fuse together dorsally.
This occurs for the most of the length EXCEPT the very cranial and very caudial ends of the tube (the far ends).
The neural folds dont fuse together at the very cranial and very caudal ends of the neural tube, allowing the formation of unclosed sections called what?
Neuropores.
The cranial neuropore closes by which day?
24
The caudal neuropore closes by which day?
26
The entire CNS develops from the walls of what?
The walls of the neural tube.
Which end of the neural tube develops into the brain?
Rostral end
Aside from the rostral end, the rest of the neural tube develops into what?
The spinal cord.
The lumen of the neural tube develops into into what 2 structures?
- ventricles of the brain
- central canal of the spinal chord
Explain what is meant by the following general terms:
neural crest cells
neural crest cells develop during neural tube fusion, towards the top (crest) of the neural tube. These cells dissociate from the tube and subsequently migrate away from it laterally.
ALL neurons with cells in the PNS develop from these neural crest cells - that is, neural crest cells are the origin of the PNS.
The population of neural crest cells may be… (3)
- transient
- multipotent
- migratory
Neural crest cells may become one of 5 different cell types. What are these 5 cell types?
- melanocytes
- craniofacial cartilage and bone
- smooth muscle
- peripheral and enteric neurons
- glia
Neural crest cells develop in close association with the underlying ________.
mesoderm
What are somites? What may somites develop into?
Somites are parts of the mesoderm (specifically they are the paraxial mesoderm), which bulge around on either side of the neural tube. Somites develop into…
- 33 individual vertebrae of spinal cord
- includes related skeletal muscle
- includes nerves that innervate this muscle
In what way are somites vital to the organisation of vertebrate embryos?
Somites are responsible for organising the segmental nature of vertebrate embryos.
In which week does brain development begin?
Fourth.
Brain development begins by the fourth week. This development includes…
a. ) Enlargements -
b. ) Bends -
a. ) Enlargements - vesicles
b. ) Bends - flexures
The primary vesicles develop at the _____ end of the neural tube.
rostral
What are the 3 primary vesicles, and what region of brain do they develop into?
- prosencephalon - forebrain
- mesencephalon - midbrain
- rhombencephalon - hindbrain, merges with spinal cord component of neural tube
The entire brain is derived from the _ ____ ____
3 primary vesicles.
When do secondary vesicles develop?
5th week
In general, where do secondary vesicles develop?
as off shoots of the primary vesicles
Secondary vesicles develop as off shoots of the primary vesicles. What are the secondary vesicles developing off of the prosencephalon?
- Telencephalon
- Diencephalon
Secondary vesicles develop as off shoots of the primary vesicles. What are the secondary vesicles developing off of the mesencephalon?
- Mesencephalon (same name)
Secondary vesicles develop as off shoots of the primary vesicles. What are the secondary vesicles developing off of the rhombencephalon?
- Myelencephalon
- Metencephalon
In total, how many secondary vesicles exist?
5
By which week does a prominent cephalic flexure form? At what level does this form?
3rd week; level of mesencephalon
By which week does a second, cervical flexure appear?
5th
The second, cervical flexure appears by the 5th week. Where does this cervical flexure appear?
At the boundary between the hindbrain and spinal cord.
What is the third flexure called? By what week does it develop?
The third flexure is the pontine flexure, which develops by week 7.
The pontine flexure is the third to develop, and it develops in week 7. Where does the pontine flexure appear?
between the metencephalon and the myelencephalon.
The neural tube becomes what 3 structures?
The primary vesicles…
prosencephalon,
mesencephalon, &
rhombencephalon
The prosencephalon (primary vesicle) develops into the telencephalon and diencephalon (secondary vesicles). What does the telencephalon become?
The cerebral hemispheres AND telencephalic vesicles also give rise to optic vesicles, which subsequently form optic stalks and cups, and eventually optic nerves and retina.
The prosencephalon (primary vesicle) develops into the telencephalon and diencephalon (secondary vesicles). What does the diencephalon become?
- thalamus
- hypothalamus
- epithalamus
- subthalamus
The mesencephalon (as a secondary vesicle) becomes what?
The midbrain.
The rhombencephalon (primary vesicle) becomes the metencephalon and myelencephalon (secondary vesicles). What does the metencephalon become?
- pons
- cerebellum
The rhombencephalon (primary vesicle) becomes the metencephalon and myelencephalon (secondary vesicles). What does the myelencephalon become?
The medulla.
Are the optic nerves and retina part of the CNS or PNS?
CNS
Do telencephalonic vesicles grow anteriorly or posteriorly?
posteriorly
Are telencephalic vesicles lateral or medial to diencephalic?
lateral
Another vesicle pair bud off the ventral surface of the cerebral hemispheres. What do these form?
olfactory bulbs and other smell related structures.
Cells of the telencephalon wall divide and differentiate into many structures. Amongst these, ____ ____ systems develop, which carry axons to and from the neurons of the telencephalon.
white matter
Explain the position of the telencephalon relative to the diencephalon.
The telencephalon is found lateral to the diencephalon. The telencephalon expands over and covers the diencephalon.
Explain what is meant by the following general term(s):
ventricle
fluid filled space
Where are lateral ventricles of the brain found?
Within the cerebral hemispheres.
Where is the third ventricle of the brain found?
Within the centre of the diencephalon.
Briefly explain the shape/ structure of the third venrtricle.
Elongated; slit like.
As the telencephalon proliferates, 2 different types of gray matter develop become apparent. What are these?
(note: this is regarding gray matter which has developed from the TELENCEPHALON ONLY! The diencephalonic gray matter is different)
- cerebral cortex (superficial gray matter)
- basal telencephalon (deep gray matter)
The diencephalon differentiates into 2 types of gray matter, what are these structures?
- thalamus
- hypothalamus
Cortical white matter involves ____ major white matter systems.
What are these systems?
3.
- cortical white matter
- corpus callosum
- internal capsule
Cortical white matter involves 3 major white matter systems - one of these is the cortical white matter system. Elaborate on this.
Simply the myelinated axons between neurons in the cerebral cortex (superficial; however not more superficial then the layer of gray matter in cerebral cortex).
Cortical white matter involves 3 major white matter systems - one of these is the corpus callosum. Elaborate on this.
- links neurons between cerebral hemispheres
- continuous with cortical white matter
- an ‘axon bridge’.
Cortical white matter involves 3 major white matter systems - one of these is the internal capsule. Elaborate on this.
- continuos with cortical white matter
- links cortex to brainstem (thalamus)
t/f: the optic vesicle is a secondary vesicle which sprouts off of the prosencephalon
true
By what day of embryological development does the neural tube form?
17/ 18.
